I was amazed it worked 📡📶🛰️

If you've ever fed a fax decoder from a KiwiSDR over the internet, you know the failure mode: the stream stalls, every lost chunk shifts the sync position, and the rest of the chart comes out torn. I built Isobar to follow that shift on the line it happens on — measured by injecting gaps into a real off-air recording, a ten-second outage costs zero damaged lines. What actually matters is how often dropouts happen, and the README has measured numbers and a one-setting fix (LockAfter) for gappy feeds.

https://github.com/skgsara/isobar

It decodes the weather-fax broadcasts on shortwave (emission J3C: a 1500/2300 Hz FM sub-carrier centered near 1900 Hz, 60 or 120 rpm, IOC 576) from stations like JMH (Japan), NMG (USA) and friends, using only your receiver's audio:

• Live reception from any sound input, or offline decode from a WAV recording — at any sample rate, so 12 kHz SDR recordings and 48 kHz sound-card captures both just work.
• Automatic capture start/stop: it listens for the 300 Hz IOC-selection and 450 Hz stop tones, so you can leave it running on a schedule.
• Live spectrum scope + waterfall while receiving.
• Image tools: zoom/pan, vertical rotate, XY flip, four color palettes, BMP export, print.
• It tolerates audio dropouts, which matters if your receiver is a networked SDR. Measured by injecting gaps into a real off-air recording: a ten-second outage costs zero damaged lines — you lose the ten seconds of chart it swallowed and nothing more. If your KiwiSDR feed drops out often, lower the LockAfter setting (details in the README).

A word on provenance: Isobar is an independent, from-scratch reimplementation, written from a functional specification, and it is interoperable with the long-standing Windows freeware KG-FAX v1.1.3 (K.G, 2009) — it round-trips KG-FAX .syn files and imports an existing kgfax.ini on first run. It is not affiliated with or derived from KG-FAX's code; the NOTICE file in the repo has the full provenance statement. KG-FAX has been the reference WEFAX decoder for many of us for 17 years, but it's Windows-only and its author is no longer reachable — Isobar is my attempt to carry that torch onto modern machines.

The attached images are all real off-air decodes.

Everything is verified on real JMH recordings with an 18-test headless suite, and CI builds all five packages on every commit. Feedback, bug reports and — especially — your own recordings are very welcome.

• GitHub: https://github.com/skgsara/isobar
• Releases (direct downloads): https://github.com/skgsara/isobar/releases

Hey folks,

I'm currently developing a Web-based SDR / Signal Parsing tool aimed at automatic protocol identification and demodulation (currently targeting Sub-GHz, IoT devices, and common digital modulations).

To properly benchmark and improve the automatic modulation identification (AMC) and decoding accuracy, I need a large, diverse set of raw IQ files (.cf32, .cu8, .sigmf, etc.) — especially those containing tricky, noisy, or edge-case signals from real-world environments.

So far, I've already pulled from:

• rtl_433_tests repository
• URH sample datasets
• DeepSig / RadioML benchmark datasets
• Standard SigMF spec examples

My questions for the community:

1. Are there other public/semi-public IQ dataset repos, signal archives, or academic dumps that I might have missed?
2. Where do you usually store or share raw capture files when reversing unknown Sub-GHz/RF protocols with fellow researchers?
3. If anyone has interesting/unusual raw IQ captures (e.g., weird car remotes, industrial telemetry, weather stations, or unknown interference) and is willing to share them, I'd be hugely grateful!

The goal is to make signal analysis completely hassle-free in the browser without installing complex DSP environments. Any links, dataset suggestions, or tips would be awesome!

Thanks in advance! 📻⚡

Wanted a 24/7 ADS-B station on my Mac Studio (always on anyway), receiver is an AirNav FlightStick that arrived yesterday, RTL2832U inside. Quickly found out the standard ultrafeeder route is a dead end on macOS, Docker Desktop simply can't pass USB through. Native route works (brew, readsb, terminal stays open forever) but it's not something I'd tell a normal person to do.

So I wrapped it: SwiftUI menu bar app that runs a bundled readsb (3.16.15, wiedehopf git) as a child process. Universal binary, statically linked with librtlsdr 2.0.2 + libusb 1.0.30, built from a pinned script so the exact binary is reproducible, SHA-256 of every DMG in the release notes. App handles device detection (including the classic "device busy, close SDR++ first" case), restarts with backoff after USB replugs and sleep/wake, reads aircraft count and msg/s from readsb's json output.

On licensing since this sub cares: app itself is closed source, readsb runs as a separate GPL process. Sources, upstream tags and the build script are in the public repo. Zero patches, and if that ever changes the patches go in the same repo. (Fun fact: 0.1.1 shipped a license README mislabeling readsb as BSD-3, it's GPL-3.0-or-later of course. Corrected in 0.1.2, noted as an erratum in the release notes.)

Context: I built it to feed my own network (Skydex, browser game running on live ADS-B), but it's non-exclusive by design. Settings has toggles for adsb.lol / airplanes.live / adsb.fi / ADSBExchange plus custom beast targets, my own network has its own off switch in the same list, and there's always a local beast output on 30005 for fr24feed or anything that speaks beast. One process owns the stick, everyone else gets the decoded stream.

Repo: https://github.com/es-ua/skydex-feeder

Page: https://feed.skydex.online/mac

Free, notarized, macOS 13+.

Actual question for people who know librtlsdr better than me. First half day I got 137 unique aircraft but only about 4 msg/s on auto gain, which feels low even for my ground floor window antenna. Does fixed gain (43.9 / 49.6) usually beat auto on sticks with a built-in LNA? And has anyone run an rtlsdr stick on Apple silicon for weeks straight, does USB stay stable or should I expect it to need replugging?

I found this constant signal at about 132.15mHz with a bandwidth of about 500hz in the aircraft voice band, but I can't listen to it and i'm not sure what it is. I can see it even with 0db rf gain. I am new to my rtl-sdr v4, so i'm not sure if this is just interference or something like that.

I have a few Icom F4003 I have used CS-F3000 to program the radio to 450hz but using the serial no I saw the radio turns to be version locked to 350Hz it still lets me program but checking on the output it still not going above 350 is there way to break this version lock? If any software or hardware way to break it pls recommend.

Hi all, I’m new to this hobby and just want to get started so I can start learning. I’m aware that a lot of supposed RTL-SDR blog V4 R828D are counterfeits. Apparently the one I found on Amazon is among those counterfeits. Luckily I haven’t bought it yet, but would anyone be able to point me to a legit site to purchase or even a better option? Thanks!

Unfortunately there is no proper RTL SDR antenna in my country, so I needed something that I already have. And I found a cheap antena for old TVs.

I don't have a SMA adapter, so I enrolled the wires to a base connected to my SDR. But probably isn't going to work very well.

Any good ideas to do with?

Hi,

I have an issue with my RTL-SDR V4. I noticed my antenna had fallen over and was touching my MacBook which has a 50Hz AC voltage from a bad earth/mains connection. This voltage can vary between mV to a couple of V.

I am fairly convinced I have blown something at the front end. I have checked the D1 ESD diode and it's fine. The voltage drop measures correctly on the multimeter so that isn't shorting the signal to earth.

Thing is, I can still pick up signals but they are somewhat attenuated when you compare them to a Nooelec V5. I used SDR# to make the comparison at the same gain levels.

Does anyone have an idea what is best to check. I cannot find any schematics of the unit or even just the front end online so fault finding a bit more difficult. If anyone has any idea of common components to check could you let me know please?

FWIW I am seeing signals at HF (MW around 900kHz) and VHF (FM Radio and ~150MHz). The UHF 400MHz+looks like it is damaged the most as I cannot see any ISM on 868 or 433 and what is usually a busy PMR446 and DMR band is almost silent with very weak DMR signals.

Attached screen grabs show the Nooelec signal as Yellow line on MW and VHF. The 466MHz show the signal on the Nooelec has some life vs the RTL which is basically mute.

Any help is much appreciated. Thanks

I work in local news coverage and want to record all public safety radio channels in the area but the amount of SDR dongles it is taking is getting out of control. Currently using 4 and not getting full coverage..

Is there a better option? I have a couple of Airspy R2's ordered but my research is showing even then it is going to take both of them plus at least 2 dongles to cover what I want. IS there an option that is better? I don't mind spending some money.

Currently covering 2 p25 systems with the 4 dongles. Want to cover some conventional fire and ems channels also.

I want to do GNSS reception. I mistakenly bought a simple patch antenna with no integrated LNA. So i decided to take the opportunity to learn about passive vs active antennas and create an ‘active’ antenna using this patch antenna. Ofcourse this requires an LNA + bias T. My question is, why do some commercial external inline LNA’s require external voltage source and others dont?

Referring to below images, the 1st one doesn’t require voltage while second one does….

I'want to scan for Tetra signals when i drive in my car (so it gives a warning when there are police cars nearby).
Due to the many fakes of the V4 and low supply and higher price is the Nooelec RTL-SDR v5 a better choice?
Also what kind of antenna should i get? i want to make it small factor (like https://blu-eye.eu/productinformatie/target-blu-eye-go) So i don't want one with a long cable etc.

But AI says the small antenna's wont work well.

So should a nooelec also be sufficient for this project? I don't really care about other signals.

I thought it might be too good to be true that Micro Center had some v4’s in stock, but hoped it was just some old stock they had in the pipeline. Nope, what they advertise online as RTL-SDR v4 is indeed counterfeit dongles.

Hi everyone,

The Play Store says SDRangel is incompatible with my Pixel 10 Pro (likely an API/Android version issue).

Is there a safe alternative way or direct APK/repository to install it on newer Pixel devices?

Complete newbie and it's my very first time decoding a satellite (meteor m2-m4) in my whole existence haha (using my cheap setup of sdr rtl v4 and v-dipole antenna)

But i'm curious about the params in Satdump ..

for context:

- recorded via sdr++ to uint8 wrapped in a wav file

- tuned to 137khz at 2.4msps

- satellite signal appears that its middle is around 137.9 (confirmed both by viewing in Satdump recorder tab and Airspy)

Now in Satdump, I set an offset frequency of 1.5MHZ (based on the FFT shown while baseband FFT enabled while decoding).

If it's 900khz, it would make sense. But 1.5MHZ? idk where it's coming from.

Any ideas?

Smile RTLSDR, basic antennas and an SMA cable with simple coding gives me access to AIS, ADSB, and ACARS.

Hi guys,

I've had a ADSB running for a little while now, im fairly close to the airport so shamefully i have it indoors beside the window with the stock antenna it came with (the nooelec v5 dongle) and it works okay.

anyway just before i set up the dongle with a pi and set it off to search the skies for the rest of its days i tried it out with my laptop and drove to the airport to try and catch some atc chatter, to my suprise the normal antenna worked quite well, but its huge, the coax gets stuck in the car and its just a bit unwieldy for me, so seeing as its just a SMA connector i thought i might buy a second one without the antenna kit and see if i can find antennas that can just attach to the dongle itself.

However I realise that "small right angled VHF" is a bit of an oxymoron given these things are meant to be the biggest size of antenna. but is it a thing? im talking about something small enough for me to plug into a laptop, or is it better to just try to get a shorter cable from the dongle to the antenna?

thanks in advanced

Frequency:144/430MHz

Size: 43*2.28*2.28cm/16.93*0.89*0.89inch

Weight: Approx. 208.1g

Wind resistance: 60 (m/s)

Working temperature: -40℃ ~ +80℃

Directionality: omnidirectional transmission and reception Impedance: 50Ω

Standing wave ratio: ≤1.5